<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <ul id="ul">
        <li onclick="alert('ok')">第1个</li>
        <li>第2个</li>
        <li>第3个</li>
        <li>第4个</li>
    </ul>
    <button id="btn">克隆</button>
    <script>
        var btnObj = document.getElementById("btn");
        var ulObj = document.getElementById("ul");
        //将第一个子元素克隆一份
        var firstObj = ulObj.children[0].cloneNode();
        // firstObj.innerHTML = "我是克隆滴";
        btnObj.onclick = function(){
            ulObj.appendChild(firstObj);
        }
    </script>
</body>
</html>